1. Field of the Invention
The present invention relates to a robot system for conveying an article using a robot.
2. Description of the Related Art
As a conveying robot system of the prior art having an industrial robot and a vision sensor, a system including a plurality of robots positioned along a conveying path of a conveyor is known. The robots are adapted to grip an article conveyed by the conveyor, and transport the article from the conveyor to another position or process. For example, Japanese Unexamined Patent Publication No. 2007-30087 discloses a system for detecting an article on a conveyor by using a vision sensor, and handling the detected article by using a plurality of robots. In this system, each robot judges whether the robot can handle the detected article or not, based on information regarding the position of the article and the number of articles to be handled. If one robot judges that the robot cannot handle an article, the robot transmits the article information to another robot on the downstream side thereof, and the robot on the downstream side handles the article. In other words, the invention of Japanese Unexamined Patent Publication No. 2007-30087 utilizes distributed control, wherein each robot controller determines which article of the detected articles should be handled by the corresponding robot.
On the other hand, International Publication No. WO2004/113030 discloses a central control, wherein one computer manages the handling process with a plurality of robots.
Although the objects to be handled in the above documents are individual articles, the above technique may be applied to a system wherein an article is contained in a container conveyed by a conveyer. However, if the above technique is applied to a system wherein a container on a conveyer has a plurality of containing segments for an article, when at least one of the containing segments is already occupied by the article, there the following problems.
It is necessary to detect each containing segment as one container. However, unlike the detection of each individual article, it is not easy to detect each containing segment in one container. In many cases, each containing segment is defined by a simple partition within a relatively large container. When an image obtained by a camera used as a sensor is processed, the feature of the image is likely to be insufficient (i.e., false-detection or misdetection may occur). In another case, a partition is not used and containing segments are conceptually defined (for example, a plurality of articles are positioned in one container in a “M-long, N-wide” configuration). In such a case, it is very difficult to detect each containing segment by a sensor.
Even if each segment can be detected, without a means for checking whether each segment is occupied by an article or not, a robot may position an article on a containing segment where another article has already been positioned. In order to avoid such a case, an operator may manually input which segment is occupied by an article. However, this is disadvantageous in view of laborsaving. As such, a system wherein a container has a plurality of segments for an article is difficult to be put to practical use.